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Test: Chemical Thermodynamics
Time : 30 minutes ........................................ Marks : 20...................... Be Fair . Look at the solutions only once you are done . Record your answers on a sheet of paper . Q.1) Fill in the Blanks : (5 Marks) 1) Work is a ________ function . 2) ∆H = ___ + ∆nRT . 3) For a reaction to be spontaneous , ∆G should be _____ . 4) Work done is maximum for ____________ process . 5) The _______ Cycle is used for calculating crystal lattice enthalpy of NaCl . Q.2) Multiple Choice Questions (5 Marks) 1) Which of the following is not state function . a) qp b) q c) enthalpy d)entropy 2) Which of the following is not an extensive property . a) Molarity b) Heat Capacity c) Mass d) Volume 3) When a sample of an idal gas is allowed to expand at constatn temperature against an atmospheric pressure , a) surroundings does work on system b) ∆U = 0 c) no heat exchange takes place d) internal energy of the system increases . 4) Which of the following conditions guarantee that a reaction is spontaneous at constant temperature and pressure . a) entropy of system increases b) entropy of system decreases c) entropy of system decreases and that of surroundings increases d) Gibbs energy of system decreases 5) A gas expands from 2L to 5L against a constant pressure of 1 atm at constant temperature . The work done by the gas will be a) 3 J b) -303.9 J c) -303.9 L.atm d) 303.9 L.atm Q.3) Define (5 Marks) 1) State Function & Path Function 2) Entropy 3)'''Second Law of Thermodynamics '''4) First Law of Thermodynamics 5)'''Third Law of Thermodynamics '''Q.4) Solve the following (Any 1) (5 Marks) 1) Three moles of idea gas are expanded isothermaly from a volum of 300 cm3 to to 2.5 L at 300 K against a pressure of 1.9 atm. Calculate the work done in L atm and Joules . 2) For a certain reaction , ∆Ho = -224 kJ and ∆So = -153 JK-1 . At what temperature will it change from spontaneous to non spontaneous ? Solutions # 1)path 2) ∆U 3)negative 4) reversible 5) Born Haber # 1) b 2)a 3)b 4)d 5)b # 1)State Function : 'The state variables do not depend on the pathway . They only depend on the state of the system . e.g. Potential Energy , Entropy . '''Path Function : '''The state variables do depend on the pathway . e.g. work , heat . 2)Entropy is the measure of disorderness . '∆S = qrev / T . 3) The Second Law of thermodynamics States that the spontaneous flow of heat is always unidirectional from higher temperature to lower temperature . Heat cannot be completely converted into an equivalent amount of work without producing permanent changes either in the system or its surroundings . The total energy of the universe increases in a spontaneous process . . . . 4) The First Law of Thermodynamics states that the energy lost from one part of the system evolves in another form , thus conserving total energy of the universe . . . 5) The third law of thermodynamics states that the entropy of a perfectly ordered crystalline substance is zero at absolute zero of temperature # 1) - 4.18 L atm , - 423.4 J 2) Spontaneous below 1464 K